Dental matrix band

ABSTRACT

The present invention relates to a dental matrix for use repairing and restoring inter-proximal cavities on a tooth with light-cured composites, the dental matrix comprising a matrix body and a plurality of light transmitting micro-pores positioned on the matrix body and overlying the inter-proximal surface of the tooth when the dental matrix engages the restored tooth. The present invention further relates to a method manufacture of such dental matrix.

FIELD OF THE INVENTION

This invention relates to a new dental matrix device for assistingdentists to form and successfully light cure composite dentalrestorations on tooth surfaces, and a method for manufacturing a newdental matrix device.

SUMMARY OF THE PRIOR ART

Matrices and the use of matrix systems are well known and widelyutilized in restorative dentistry. There are many types of matricesavailable and are generally made entirely of metal or plastic and aresectional or circumferential bands. Plastic matrices generally arethicker than metal matrices and this causes problems obtaining tightinter-proximal contacts. For this reason, metal matrices have been morepopular for posterior teeth.

During the restoration of an inter-proximal cavity, the matrix band issecured around the tooth and cavity and forms a mould. This mould isfilled with composite material and the composite is light cured. Thedifficulty with curing an inter-proximal restoration is that once themetal matrix band is wrapped around the tooth, the matrix band does notallow horizontal curing of the composite at the gingivo-proximal toothsurface. It has to be cured from above and this can lead to incompletecuring of the composite resin. When this occurs, composite resin canadhere to the metal matrix rather than the tooth and detach from therestoration when the matrix is removed. The restoration must then bere-done or repaired.

Prior art exists of metal matrices with one or two open areas coveredwith a membrane of transparent material and of matrices withilluminating ports with port covers. These open areas and ports cover arelatively large area of the matrix and because these openings areeither covered by a port cover or covered by a very thin expanding film,in-use, they may result in restorations with poor anatomical form.

It is an object of the present invention to provide the dentist with ameans of firmly retaining the composite material with a metallic matrixwhile enabling light curing of the composite, or to at least providedental practitioners with a useful choice.

SUMMARY OF THE INVENTION

In a first aspect the invention consists in a dental matrix for use inrepairing and restoring cavities with light-cured restorative material,the dental matrix comprising:

-   -   a metal substrate comprising a plurality of micro-apertures,        wherein the micro apertures are filled with a transparent or        semi transparent resin, and    -   a polymer layer covering the metal substrate and the resin        filled micro-apertures for contacting the tooth in use.

In some embodiments the transparent or semi-transparent resin used tofill the micro-apertures is also used to form the polymer layer coveringthe metal substrate.

In some embodiments the polymer layer is formed of a polymer that doesnot stick to the dental restorative material, the polymer layer forminga smooth non-stick surface finish.

In some embodiments the polymer layer is a fluorocarbon. In someembodiments the fluorocarbon is polytetra-fluoroethylene. In someembodiments the fluorocarbon is fluorinated ethylene propylene. In someembodiments the fluorocarbon is perfluoroalkoxy.

In some embodiments the polymer layer has a thickness of 25 micron orless.

In some embodiments the dental matrix comprises a layer of the resin ona side of the dental matrix opposite the polymer layer. In someembodiments the dental matrix has no layer of resin on a side of thedental matrix opposite the polymer layer.

In some embodiments the metal substrate is a foil.

In some embodiments the metal substrate is a stainless steel substrate.

In some embodiments the metal substrate has a thickness of 20-50 micron.

In some embodiments each of the plurality of micro-apertures has an areaof between 300 and 80,000 square microns.

In some embodiments the plurality of micro-apertures comprises circularmicro-apertures.

In some embodiments the plurality of micro-apertures comprises hexagonalmicro-apertures. In some embodiments the plurality of micro-aperturescomprises oval micro-apertures. In some embodiments the plurality ofmicro-apertures comprises elongate micro-apertures or slots each havinga length greater than a width. In some embodiments a width of each ofthe elongate micro-apertures or slots is 50 to 180 micron. In someembodiments each elongate aperture has a length and a width and a ratioof the length and the width is 1.2 to 5. In some embodiments the ratioof the width of each of the plurality of micro-apertures and thethickness of the metal substrate is greater than 2. In some embodimentsthe ratio of the width of each of the plurality of micro-apertures andthe thickness of the metal substrate is greater than 3. In someembodiments each of the plurality of micro-apertures is circular and 20to 180 micron in diameter. In some embodiments the ratio of the diameterof each of the plurality of micro-apertures and the thickness of themetal substrate is greater than 2. In some embodiments the ratio of thediameter of each of the plurality of micro-apertures and the thicknessof the metal substrate is greater than 3.

In some embodiments the micro-apertures are arranged in a concentricarchway pattern. In some embodiments the micro-apertures are arranged ina honeycomb pattern. In some embodiments the plurality ofmicro-apertures comprises elongate micro-apertures each having a lengthgreater than a width, and at least some of the elongate micro-aperturesbeing arranged in concentric rings about a centre or centre region eachwith its length aligned approximately towards the centre or centreregion. In some the centre or centre region may be located on the dentalmatrix to be positioned between the lingual side of the tooth and thebuccal side of the tooth in use. In some the centre or centre region ispositioned on the dental matrix, in use the elongate micro-apertureslocated above the centre each with its length aligned approximatelytowards the centre or centre region and the elongate micro-apertureslocated below the centre each with its length aligned approximatelyhorizontally. In some embodiments the elongate micro-apertures locatedbelow the centre are arranged in columns. In some embodiments the centreis located adjacent a bottom edge of the dental matrix. In someembodiments the plurality of micro-apertures comprises two groups ofmicro-apertures, each group of micro-apertures comprising elongatemicro-apertures each having a length greater than a width, and at leastsome of the elongate micro apertures being arranged in concentric ringsabout a centre or centre region each with its length alignedapproximately towards the centre or centre region. In some embodimentsthe two groups of micro-apertures are located either side of a centreline of the dental matrix.

In some embodiments the thickness of the dental matrix is less than 60micron. In some embodiments the thickness of the dental matrix is lessthan 50 micron. In some embodiments the thickness of the dental matrixis less than 45 micron.

In some embodiments the dental matrix is a sectional matrix. In someembodiments the dental matrix is a shaped circumferential band. In someembodiments the dental matrix is a straight edged circumferential band.

In a second aspect the invention consists in a dental matrix for use inrepairing and restoring cavities with light-cured restorative material,the dental matrix comprising:

-   -   a metal substrate comprising a plurality of micro-apertures,        wherein the plurality of micro-apertures comprises elongate        micro-apertures each having a length greater than a width, and        at least some of the elongate micro apertures being arranged in        concentric rings about a centre or centre region each with its        length aligned approximately towards the centre or centre        region.

In some embodiments the centre or centre region may be located on thedental matrix to be positioned between the lingual side of the tooth andthe buccal side of the tooth in use.

In some embodiments the centre or centre region is positioned on thedental matrix, in use the elongate micro-apertures located above thecentre each with its length aligned approximately towards the centre orcentre region and the elongate micro-apertures located below the centreeach with Its length aligned approximately horizontally.

In some embodiments the elongate micro apertures located below thecentre are arranged in columns.

In some embodiments the centre is located adjacent a bottom edge of thedental matrix.

In some embodiments the plurality of micro-apertures comprises twogroups of micro-apertures, each group of micro-apertures comprisingelongate micro-apertures each having a length greater than a width, andat least some of the elongate micro apertures being arranged inconcentric rings about a centre or centre region each with its lengthaligned approximately towards the centre or centre region.

In some embodiments the two groups of micro-apertures are located eitherside of a centre line of the dental matrix.

In some embodiments the micro-apertures are arranged in a concentricarchway pattern.

In a third aspect the invention consists in a method of forming a dentalmatrix for use in repairing and restoring cavities in a tooth withlight-cured composites, the method comprising:

-   -   i) providing a metal substrate,    -   ii) coating a side of the metal substrate with a polymer to form        a polymer layer on a side of the dental matrix for contacting        the tooth in use,    -   iii) forming micro-apertures in the metal substrate by photo        etching a reverse side of the metal substrate without breaking        the polymer layer.

In some embodiments the method comprises:

-   -   iv) filling the micro-apertures with a transparent or        semi-transparent resin.

In some embodiments the method comprises applying the resin to the metalsubstrate by an apparatus that simultaneously fills the micro aperturesand removes substantially all resin from the reverse side of the dentalmatrix. In some embodiments the method comprises applying the resin tothe metal substrate by an apparatus that simultaneously fills the microapertures and leaves a layer of resin on the reverse side of the dentalmatrix.

In some embodiments the apparatus comprises one or more of a roller anda squeegee or blade like apparatus.

In some embodiments the method comprises providing a parent metalsubstrate and subsequently separating the dental matrix from the parentmetal substrate.

In some embodiments the method comprises photo etching at least aportion of a perimeter of the dental matrix for separating the dentalmatrix from the parent metal substrate, and separating the dental matrixfrom the parent metal substrate by breaking the polymer coating at theperimeter of the dental matrix.

In some embodiments the method comprises adding a photo-resistive filmto the reverse side of the metal substrate after the coating is added tothe metal substrate.

In some embodiments the method comprises providing the parent metalsubstrate as a metal strip.

In some embodiments the metal strip is provided in a coil, and themethod comprises unwinding the metal strip from the coil for the polymerlayer to be applied.

In some embodiments the method comprises spraying the polymer onto asurface of the metal substrate, and heating the metal substrate withsprayed polymer In an oven to form the polymer layer on the metal strip.

In some embodiments the method comprises applying the resin to the metalsubstrate using a squeegee or blade like apparatus for spreading theresin into the apertures.

In some embodiments the method comprises applying the resin to the metalsubstrate using a squeegee or blade like apparatus for spreading theresin into the apertures and to leave a layer of resin on the reverseside of the dental matrix. In some embodiments the method comprisesapplying the resin to the metal substrate using a squeegee or blade likeapparatus for spreading the resin into the apertures and tosubstantially remove all resin from the reverse side of the dentalmatrix.

In some embodiments the polymer is a fluorocarbon to form a fluorocarbonlayer. In some embodiments the polymer is polytetra-fluoroethylene toform a polytetrafluoroethylene layer.

In some embodiments the polymer layer has a thickness of 25 micron orless. In some embodiments the method comprises the resin is one of afluorocarbon, polytetra-fluoroethylene, a polyester.

In some embodiments the method comprises the metal substrate is a foil.

In some embodiments the method comprises the metal substrate is astainless steel substrate.

In some embodiments the method comprises the metal substrate has athickness of 20-50 micron.

The term “comprising” as used in this specification and claims means“consisting at least in part of”. When interpreting each statement inthis specification and claims that includes the term “comprising”,features other than that or those prefaced by the term may also bepresent. Related terms such as “comprise” and “comprises” are to beinterpreted in the same manner.

It is Intended that reference to a range of numbers disclosed herein(for example, 1 to 10) also incorporates reference to all rationalnumbers within that range (for example, 1, 1.1, 2, 3, 3.9, 4, 5, 6, 6.5,7, 8, 9 and 10) and also any range of rational numbers within that range(for example, 2 to 8, 1.5 to 5.5 and 3.1 to 4.7) and, therefore, allsub-ranges of all ranges expressly disclosed herein are hereby expresslydisclosed. These are only examples of what is specifically intended andall possible combinations of numerical values between the lowest valueand the highest value enumerated are to be considered to be expresslystated in this application in a similar manner.

The invention consists in the foregoing and also envisages constructionsof which the following gives examples only.

BRIEF DESCRIPTION OF THE DRAWINGS

A preferred embodiment of the present invention will now be describedwith reference to the accompanying drawings in which;

FIG. 1 illustrates a dental matrix according to one embodiment of thepresent invention.

FIG. 2 illustrates a dental matrix according to another embodiment ofthe present invention.

FIG. 3 illustrates a schematic part cross section of a dental matrixaccording to one embodiment of the present invention.

FIG. 4 illustrates a schematic part cross section of a dental matrixaccording to another embodiment of the present invention.

FIG. 5 illustrates a shaped circumferential band dental matrix accordingto another embodiment of the present invention.

DETAILED DESCRIPTION OF THE PRESENT INVENTION

A dental matrix band comprising features of the present invention isdescribed with reference to FIGS. 1 to 3. FIG. 1 shows a firstembodiment of the present invention consisting of a sectional matrix,and FIG. 2 shows an alternative embodiment. FIG. 3 shows a cross sectionthrough a dental matrix comprising features of the present invention.Whenever possible, common reference numbers will be utilized to refer tocommon elements and features in each of the embodiments described.

Each dental matrix 10 illustrated in FIGS. 1 and 2 comprises a matrixbody 12 having a tab 14 with a first bore 16 disposed on the top borderof the matrix body 12 and a second and third bore 18, 20 disposedadjacent to either side edge of the matrix body 12. Tab 14 provides thedentist with a section of material where the matrix can be grabbed witha dental instrument and moved into or out of position in the patient'smouth. The first, second and third bores 16, 18, 20 further assist inthe dentist in placing, positioning, and extracting the matrix 10 andare particularly useful when the dentist is using a pinned tweezers orother dental instrument having a pin or hook for attaching to variousitems. The matrix body 12 terminates at its lower margin at a flangeportion 22 at the lower portion of the matrix body 12. The flangeportion 22 addresses the tooth being restored at the gingival margin.While the dental matrices 20 shown each includes a gingival flangeportion 22, tab 14 and holes 16, 18 and 20, it is contemplated that thedental matrix can be manufactured with only a dental matrix body 12 andwithout a gingival flange portion or tab 12 or holes 16, 18 and 20without falling outside the scope of the invention. When the dentalmatrix 10 is without a gingival flange portion, the bottom edge of thedental matrix body 12 forms the bottom edge of the dental matrix 10.

In one embodiment, the matrix body 12 exhibits a degree of curvaturealong both its longitudinal axis (horizontal axis in use) andlatitudinal axis (vertical axis in use), thus enabling the matrix body12 to be formed into a shape complementary with and against a tooth berestored.

The matrix body 12 is formed from a metal substrate or foil 13, forexample a stainless steel foil. Preferably the metal substrate has athickness of 20 to 50 micron (micrometre, pm).

As shown in FIGS. 1 and 2, the matrix body 12 further comprises aplurality of light-transmitting micro-apertures 24, 26. Preferably themicro-apertures generally cover a majority of the matrix body 12 andflange portion 22, and at least an area of the matrix body that in useoverlays the inter-proximal surface of a tooth to be restored.

The micro-apertures 24, 26 are positioned on the matrix body 12 andgingival flange portion 22 such that when the matrix 10 is formed intothe desired configuration around the tooth being restored, themicro-apertures 24, 26 align with the interproximal tooth surface of thetooth being restored.

In the embodiment shown in FIG. 2, each micro-aperture is substantiallycircular and is approximately 20 to 180 micron in diameter. In oneembodiment a ratio of the diameter of the micro-apertures and thethickness of the metal substrate of the matrix is greater than 2. Inanother embodiment a ratio of the diameter of the micro-apertures andthe thickness of the metal substrate of the matrix is greater than 3.When light is shined through the matrix, the thickness of the matrix andthe aperture size determines the amount of light that can pass throughthe matrix for a given angle 15 of incidence of light to the plane ofthe matrix. For example, for a ratio of greater than 2, the angle ofincidence for light to pass through the matrix must be greater thanabout 27 degrees. For a ratio of greater than 3, the angle of incidencefor light to pass through the matrix must be greater than about 19degrees.

The micro-apertures can be different shapes and configurations,including elongated apertures such as slots as shown in the embodimentof FIG. 1, hexagonal shaped apertures or oval apertures (notillustrated) for example.

Referring to the embodiment of FIG. 1, the micro-apertures 24 consist ofelongated apertures or slots having a length of approximately 50 to 180micron. Preferably the length is 1.2 to 5 times the width of the slots.In one embodiment a ratio of the width of the micro-apertures and thethickness of the metal substrate of the matrix is greater than 2. Inanother embodiment a ratio of the width of the micro-apertures and thethickness of the metal substrate of the matrix is greater than 3.

The micro-apertures 24, 26 can be arranged in a number of differentconfigurations. In FIG. 2, the substantially circular micro-aperturesare arranged in a staggered or honey comb configuration 5. In analternative embodiment the micro-apertures may be aligned in columns.

In the embodiment of FIG. 1, at least some of the slots 24 are arrangedin concentric rings 4 about a centre or centre region 25, each slot withits length aligned approximately towards the centre. The arrangement ofapertures 24 in the embodiment of FIG. 1 may be described as aconcentric archway pattern. As illustrated, the centre may be locatedcentrally between side edges of the dental matrix, or located betweenthe lingual side of the tooth and the buccal side of the tooth to betreated in use.

As shown in FIG. 1, the centre 25 may be positioned on the dental matrix(within the perimeter of the dental matrix). In the illustratedembodiment, the slots located above the centre 25 are each arranged withits length aligned approximately towards 10 the centre 25. The slotslocated below the centre each have its length aligned approximatelyhorizontally. As shown, the slots arranged horizontally are formed incolumns, however these slots may be arranged in a staggered arrangement,like the circular apertures in the embodiment of FIG. 2. Further, theapertures below the centre, for example on the area of the flangeportion 22, may be other shapes, for example circular. In a furtheralternative embodiment that does not comprise a flange portion 22, thecentre 25 of the aperture pattern may be located at or near to a bottomedge of the matrix. In a further alternative embodiment, non-elongatedmicro apertures may be arranged in a concentric archway pattern. Forexample, circular apertures may be formed in a concentric archwaypattern with the circular apertures arranged in concentric rings about acentre or centre region.

The alignment of the slots or elongate apertures (for example oval orother elongated shape) in the embodiment illustrated in FIG. 1facilitates light entry of tight beams from a curing light source intothe micro-apertures at an angle from above normal to the plane of thematrix. The micro-apertures also allow light to enter from substantiallyhorizontal to the plane of the matrix. Arranging elongatedmicro-apertures in the circular manner with respect to a centre 25reduces or eliminates the need to align the light source directlyperpendicular or normal to the matrix, which becomes increasinglydifficult as the micro-apertures fall further into the inter-proximalspace, while still enabling maximum light transmission through thedental matrix.

It is desired that that the interior surface of the matrix 10 be smoothand free from blemishes or imperfections that may transferred to thecomposite material and formed into the restoration. To maintain thesmooth interior surface of the matrix 10 that contacts the tooth in use,the individual micro-apertures are filled with a transparent, lighttransmitting material 28, as illustrated in the cross sectional view ofFIG. 3. Preferably, the micro-apertures are filled with a resin orpolymer, for example one of a fluorocarbon or a polyester. It iscontemplated that any suitable transparent or semitransparent, lighttransmitting material may be used to fill the micro-apertures. Asuitable resin may have a compressive strength of about 7,000 psi (ASTMD695). A suitable resin may have a flexural modulus of about50,000-65,000 psi (ASTM D790). A suitable resin may have a tensilestrength of about 3,000 psi to 6,000 psi (ASTM D638). A suitable resinmay have an elongation of about 25% (ASTM D2370). The resin may comprisea urethane resin. The resin may comprise compounds to enhance releaseproperties. For example the resin may comprise one or more ofco-polymerisable silicone and polyethylene wax. The resin may comprisecomponents to enhance adhesion to the substrate. For example the resinmay comprise an acid coupling agent.

In one embodiment illustrated in FIG. 4, the apertures 24 are filledwith resin and a resin layer 29 is also formed or provided to theexterior surface of the matrix that does not contact the tooth to betreated in use. In the embodiment illustrated in FIG. 3, there is noresin layer or a very thin resin layer on the exterior surface of thematrix. This form of the matrix provides a thinner matrix which ispreferred.

Preferably the thickness of the matrix illustrated in either FIG. 3 or 4is less than 60 micron. More preferably the thickness is less than 50micron, and most preferably the thickness is less than 45 micron, forexample a thickness of around 40 micron.

Also, as illustrated in FIG. 3, a transparent, light transmitting film30 is provided to the surface of the dental matrix 10 that contacts thetooth in use. The film or layer 30 covers the metal substrate 13 and theresin filled micro apertures and presents a smooth surface 31 forcontact with the tooth. Preferably, the film 30 is a polymer layer, forexample a fluorocarbon layer such as polytetra-fluorocarbon, for example5 Dupont's Teflon®, Whitford Corporation's Xylan® or other suitablealternative material such as fluorinated ethylene propylene, orperfluoroalkoxy. Preferably the polymer layer is formed of a polymerthat does not stick to the dental restorative material so that thepolymer forms a non-stick smooth surface finish. In one embodiment, thepolymer layer 30 is formed from the resin used to fill themicro-apertures. Preferably the thickness of the polymer layer is 25micron or less.

An alternative matrix is illustrated in FIG. 5. The matrix of FIG. 5 isa shaped circumferential band. The matrix of FIG. 5 comprises a groupingof micro-apertures positioned to one side of a centre line 42 of thematrix. In the illustrated embodiment, the matrix comprises twogroupings of micro-apertures 24A and 24B. Each grouping of microapertures comprises a concentric archway pattern as described withreference to the embodiment of FIG. 1. Each grouping 24A and 24Bcomprises slots arranged in concentric rings 4 about a centre or centreregion 25, each slot with its length aligned approximately towards thecentre. In use, the centre 25 of each grouping of apertures may belocated between the lingual side of the tooth and the buccal side of thetooth to be treated, or on the lingual side of the tooth or the buccalside of the tooth to be treated.

Other variations described with reference to the embodiment of FIG. 1may be incorporated into a circumferential matrix band as described withreference to the embodiment of FIG. 5.

The new dental matrix 10 operates in the following manner. First, thedentist prepares an inter-proximal cavity on the surface of the toothbeing restored to receive the light-cured composite/restorationmaterial. The dental matrix 10 is then inserted into the interproximalspace and held securely against the tooth being restored with aretaining device. Next, to ensure there is no leaking of the compositebetween the dental matrix 10 and tooth, a dental wedge may be insertedinto the inter-proximal space to hold the dental matrix 10 firmlyagainst the surface of the tooth being restored. The wedge may beinserted before or after a retaining device is applied to hold thematrix in place. Once the dental matrix 10 is secured in position, thecavity is then filled with composite material. Finally, the composite islight-cured from an occlusal direction as per normal but can also becured horizontally through the micro-apertures in the dental matrix.

Method of Manufacture

A method for manufacturing a dental matrix band comprising features ofthe present invention is described below.

A metal substrate is coated on one side with a film or layer 30.Preferably the metal substrate has a thickness of 20 to 50 micron, Toapply the layer 30 on the substrate, the coating material 30 may besprayed on to a surface of the metal substrate. For example, afluorocarbon such as polytetra-fluorocarbon, for example Dupont'sTeflon® is sprayed onto a surface of the metal substrate. The appliedcoating and metal substrate is preferably baked in an oven to dry or setthe coating material on the substrate to form the film or layer 30. Forexample the substrate and applied coating material is baked in an ovenat a temperature of about 360° C. to about 400° C. In some embodiments,the substrate with coating is baked or cured in an oven for about 30seconds or less than 30 seconds. In some embodiments, the metalsubstrate is preheated before the coating material is applied. Forexample, the metal substrate is preheated in an oven at a temperature ofabout 400° C. to about 420° C. In some embodiment, the metal substrateis preheated for period of about 10 seconds, or less than 10 seconds. Insome embodiments, the substrate with coating is subjected to apre-drying process by heating with infrared radiation prior to baking inan oven. In some embodiments, the coating is heated by infraredradiation at about 100° C., or about 90° C. to 100° C. In someembodiments, the substrate with coating is preheated by infraredradiation for a period of about 20 seconds, or less than 20 seconds.Preferably the coating has a thickness of less than about 25 microns.

After the coating has been applied to the metal substrate,micro-apertures 24, 26 are formed in the metal substrate by photoetching the metal substrate from a reverse or opposite side of the metalsubstrate.

A reverse or opposite side to the coated side of the metal substratecomprises a photo-resisting film. The photo resistive film or layer maybe applied before or after the coating 30 is applied to the metalsubstrate. For example, a side of the metal substrate is cleaned with acleaning solution, for example a caustic degreaser. The cleaned surfaceis then coated with a UV light sensitive photo resist. A stencil and/orimaging system may be used to expose a desired configuration for themicro-apertures on the photo resistive film. Other features of thematrix may also be exposed on the photo resist. Exposure, for exampleusing UV light, prepares areas of the resisting film to form a resistantfilm on the surface of the substrate. The substrate is then washed, forexample with a developing solution, to wash away unexposedphoto-resisting film to expose the metal substrate according to apattern produced by the stencil or imaging system. Areas of the exposedphoto resist remain on the surface of the metal substrate. Thephoto-resist film and developing solution may be any suitablecommercially available films and solutions suitable for use in the photoetching process. The metal substrate with developed film is 10 thenetched to dissolve the metal exposed through the photo restive film. Forexample the metal substrate with developed resistive film and coating 30is placed in a etching bath and the exposed metal of the substrate isremoved by chemical etching. The etchant may be an aqueous solution ofacid, for example ferric chloride. In one embodiment the etchant isheated and directed under pressure at the substrate coated withdeveloped photo resist film. The etchant reacts with the unprotectedsurfaces of the metal substrate to corrode the metal quickly. Afteretching, the metal substrate with coating 30 is washed and rinsed toneutralize and/or remove the etchant. The etched metal substrate may becleaned and dried. Photo resist film remaining on the surface of themetal substrate may be removed, for example by chemically removing thephoto resist layer with a suitable resist stripper, and the metalsubstrate comprising micro-apertures may be cleaned and dried.

In some embodiments the polymer coating is not affected by the chemicalsused in the etching process. Therefore the photo etching process forforming the micro-apertures does not damage the coating on the surfaceof the metal substrate 30. Therefore the manufacturing process describedproduces a matrix band comprising metal substrate with micro-apertures,and a polymer layer covering a side of the metal substrate and the microapertures in the metal substrate. The micro-apertures are etched awayleaving only a layer of polymer over each micro-aperture.

Preferably a parent metal substrate is prepared with a plurality ofmatrix bands for subsequent division from the parent metal substrateinto individual matrix bands comprising the metal substrate with microapertures and polymer coating. For example, in some embodiments, acontinuous strip of metal substrate is coated with polymer. In someembodiments, a continuous strip metal substrate is passed through acontinuous coating line. In some embodiments a continuous coating linecomprises one or more of preheating the metal strip, spray coating thestrip with a polymer coating, infrared pre-drying and oven curing. Thepolymer coated strip is then passed through the photo etching process toprepare many dental matrices along the strip. Following the etchingprocess the strip may be passed through a press-tool and/or cutting diesto stamp each matrix from the strip. For example, a press tool is may beconfigured to accept a continuous strip being fed into the tool by atractor-feed mechanism. In some embodiments, in a stamping process3-dimensional forms can be pressed into the metal substrate.

In some embodiments, an outline or perimeter of the matrix band isetched in the photo etching process. The perimeter of the matrix may beincorporated into the stencil and/or imaging system to be etchingtogether with the etching of the micro-apertures. For example,substantially the full perimeter of the matrix band can be etched, orthe full perimeter of the matrix band may be etched. Where the fullperimeter of the matrix band is etched, each individual matrix band maybe retained in position in the parent metal substrate by the polymercoating. Each individual matrix may be separated from the parentsubstrate by breaking or cutting the polymer coating at the perimeter ofthe matrix. For example, the matrix may be pressed out with a formingtool for forming the matrix into a 3-dimensional configuration. In someembodiments, the matrix is shaped by a first conventional press tool,and pushed out of the parent material by a second forming tool. Theperimeter of the matrix may be shaped to include tabs 14. Otherfeatures, for example holes 16, 18 and 20 may be etched in the photoetching process. By etching away the outline periphery of the matrix,the matrix is separated from the parent metal substrate without therequirement for cutting dies or the like. Press tooling and cutting diesrequire frequent repair and maintenance. Their elimination can result inan improvement in manufacturing efficiency, and/or savings inmanufacturing costs.

The manufacturing method enables the production of micro apertures inthe matrix that are covered on one side by a polymer layer. Themicro-apertures allow light to pass through making the metal matrix‘transparent’.

In some embodiments the method comprises filling the micro apertureswith resin 28. In some embodiments the resin is applied to the metalsubstrate by an apparatus that simultaneously fills the micro aperturesand removes substantially all resin from the reverse side of the dentalmatrix. In some embodiments the resin is applied to the metal substrateby an apparatus that simultaneously fills the micro apertures and leavesa thin layer 30 of resin on the reverse side of the dental matrix. Insome embodiments the resin may be spread over the surface and forcedinto the micro apertures by a roller or rollers. The metal substratecomprising micro-apertures and polymer coating and with resin applied tothe reverse side of the metal substrate may be passed through rollersfor forcing the resin into the micro apertures. In some embodiments theresin may be provided to a roller and the roller being in contact withthe reverse side of the matrix presses the resin into the apertures. Insome embodiments the roller may leave a thin layer 30 of resin on thereverse side of the dental matrix. In some embodiments, the roller mayremove substantially all resin from the reverse side of the dentalmatrix to achieve the cross section illustrated in FIG. 3. In someembodiments the resin may be applied to the metal substrate using asqueegee or blade like apparatus for spreading the resin into theapertures. In some embodiments, the squeegee may leave a thin layer 30of resin on the reverse side of the dental matrix. In some embodiments,the squeegee may remove substantially all resin from the reverse side ofthe dental matrix to achieve the cross section illustrated in FIG. 3. Insome embodiments a squeegee or blade like instrument is used to removerecess resin from the reverse side of the dental matrix after the resinhas been provided to the micro-apertures, for example by a roller orrollers. Preferably the micro-apertures are filled with resin prior toseparating the dental matrix from the parent metal substrate. In theembodiment illustrated in FIG. 4, the layer of resin 4 is broken or cutat the perimeter of the dental matrix to separate the dental matrix 20from the parent substrate.

The foregoing description of the invention includes preferred formsthereof. Modifications may be made thereto without departing from thescope of the invention as defined by the accompanying claims.

1. A method of forming a dental matrix for use in repairing andrestoring cavities in a tooth with light-cured composites, the methodcomprising: i) providing a metal substrate, ii) coating a side of themetal substrate with a polymer to form a polymer layer on a side of thedental matrix for contacting the tooth in use, iii) formingmicro-apertures in the metal substrate by photo etching a reverse sideof the metal substrate without breaking the polymer layer.
 2. The methodof claim 1, comprising: iv) filling the micro-apertures with atransparent or semi-transparent resin.
 3. The method of claim 2,comprising applying the resin to the metal substrate by an apparatusthat simultaneously fills the micro apertures and removes substantiallyall resin from the reverse side of the dental matrix.
 4. The method ofclaim 3, wherein the apparatus comprises one or more of a roller and asqueegee or blade like apparatus.
 5. The method of claim 1, comprisinga) providing a parent metal substrate and subsequently separating thedental matrix from the parent metal substrate, b) spraying the polymeronto a surface of the metal substrate, and heating the metal substratewith sprayed polymer in an oven to form the polymer layer on the metalstrip
 6. The method of claim 5, comprising photo etching at least aportion of a perimeter of the dental matrix for separating the dentalmatrix from the parent metal substrate, and separating the dental matrixfrom the parent metal substrate by breaking the polymer coating at theperimeter of the dental matrix.
 7. The method of claim 1, comprisingadding a photo-resistive film to the reverse side of the metal substrateafter the coating is added to the metal substrate.
 8. The method ofclaim 5, wherein the parent metal substrate is a metal strip.
 9. Themethod of claim 2, comprising applying the resin to the metal substrateusing a squeegee or blade like apparatus for spreading the resin intothe apertures.
 10. The method of claim 9, comprising applying the resinto the metal substrate using a squeegee or blade like apparatus forspreading the resin into the apertures and to leave a layer of resin onthe reverse side of the dental matrix.
 11. The method of claim 9,comprising applying the resin to the metal substrate using a squeegee orblade like apparatus for spreading the resin into the apertures and tosubstantially remove all resin from the reverse side of the dentalmatrix.
 12. The method of claim 5, wherein the parent metal substrate isa metal strip provided in a coil, and the method comprises unwinding themetal strip from the coil for the polymer layer to be applied, whereinthe polymer is a fluorocarbon to form a fluorocarbon layer orpolytetrafluoroethylene to form a polytetrafluoroethylene layer, whereinthe polymer has a thickness of 25 micron or less, wherein the resin isone of fluorocarbon, polytertrafluoroethylene, or polyester, wherein themetal substrate is a foil or a stainless-steel substrate and wherein themetal substrate has a thickness of 20-50 microns.